Fouling is a common problem in water-based systems. Fouling can occur in a component in the system, such as in a heat exchange, a reactor or in a section of pipe or conduit in the system. Fouling can also occur in a component of a device in the system, such as a membrane in a filtration module. For example, fouling of filtration modules in high quality water production plants and industrial heat exchangers is a major operational problem in such systems. Membrane fouling can result in decreases in production (reduced water production, reduced heat transfer); increases in operational energy demands; costly system outages due to cleaning/de-fouling of the membrane; increased costs of system maintenance; and overall aging/wear on the systems.
Failure to timely clean components in water-based systems can result in higher cleaning costs (e.g. longer cleaning times, additional cleaning agents, use of more aggressive cleaning agents, etc.) and premature component replacement. For example, loss of operating time and increased costs associated with membrane cleaning and premature filtration module replacement along with reduced operating performance result in overall increased separation costs. Thus, it is important to carefully monitor fouling in order to optimize system performance, cleaning and component longevity.
Fouling of components in water-based systems is a physiochemical phenomenon that occurs when one or more of the components become coated or blocked by an accumulation of one or more various materials, foulants. The foulants can be from a variety of sources: inorganic, organic, colloidal, microbial, etc.; and each type of foulant can be most readily removed by different cleaning procedures. Identification of both the amount and the type of foulant can thus be important in selecting an appropriate cleaning treatment.
Filtration modules and heat exchangers are examples of closed non-transparent components usually operating under high pressure/high temperature. Direct measurements and monitoring systems to detect and determine the fouling type of closed components in operation are not available. These difficulties are especially true for spiral wound module configurations. Spiral wound membrane modules are a particularly important filtration technique for the production of high quality drinking water from seawater. Due to their spiral configuration, it is difficult to visually inspect the membrane surface without destroying or otherwise compromising the integrity of the module. Fouling detection and analysis in these modules are based on monitoring operational parameters like pressure drop along the modules, permeate production/heat transfer etc. When one or multiple parameters exceed a predefined threshold cleaning is applied. Indirect measures including permeate flow rates, permeate recovery ratios, operating pressures, feed temperatures and permeate quality can be influenced by factors unrelated to membrane fouling, such as concentration polarization.
Further, current systems are not sensitive enough to indicate fouling at an early stage and further do not provide sufficient information concerning the type of fouling that is needed to determine the fouling treatment method(s) needed. Typically determination of the type of fouling requires removal and opening of a component, and samples taken and analyzed in a laboratory.